Generally it requires a strobe dimmer having variable luminous intensity and color temperature to take a good photo.
Presently, several strobe dimmers are known for obtaining variable luminous intensity and color temperature.
For example, the patent KR-29301 filed Jul. 30,1986, by the same applicant discloses a strobe dimmer as shown in FIG. 1. According to this document, strobe discharge tube(ST1,ST2) are connected through respective connector. A fourfold-voltage rectifier circuit (1) in a charger and discharger connected to the other side of the connector, consists of two double-voltage rectifier(11,12) so to output double or fourfold rectified voltage depending on applied power(AC). The fourfold-voltage rectifier circuit(1) rectifies input voltage to fourfold DC voltage and then offers respective outputs to output terminals(X,Y), wherein the outputs are 620 V DC and 310 V DC respectively when the power supply is 110 V. On the other hand, in the case of 220 V, said rectifier circuit(11) just rectifies the input voltage to double DC voltage and then offers same output(i.e., 620 V DC and 310 V DC) to the terminals(X,Y) thereof respectively.
The power supply(AC) is applied to the fourfold-voltage rectifier(1) through a resistor(R2) and a terminal(B), and also applied to a third relay(RY3) through a resistor(R3) and a diode(D1) of a 110 V/220 V automatic switching circuit(3), when 110 V power supply is applied by turn on a power supply switch(SW1). Since the third relay(RY3) is operated by 220 V-power supply, when 110 V power supply is applied to a third relay(RY3), a relay switch turns off to block the current to a gate of a triac(TC2). Therefore, the triac(TC2) is cut off and a fourth relay(RY4) may not operate, so that a terminal(b) in the relay switch of the fourth relay is connected to a terminal(c) and a terminal(e) is connected to a terminal(f) respectively. Furthermore, 110 V AC power is supplied to the primary intermediate tap of transformer(T1) through the respective relay switches(e,f) of the fourth relay(RY4) to apply increased AC voltage on the secondary of the transformer.
Since the increased AC voltage is applied to the well-known high voltage generating circuit(5) for trigger voltage, a terminal(S) of the high voltage generating circuit(5) outputs high voltage. AC power applied between the terminal(B) and a ground terminal of the fourfold rectifier circuit(1) is rectified to fourfold voltage in the usual manner. Since the fourth relay(RY4) of 110 V/220 V automatic switching circuit(3) is connected to the relay switch terminals(b,c) of said fourth relay switch(RY4) in non-operating state, the double-voltage rectifier circuit(11) is connected to the other double-voltage rectifier circuit(12) through the relay switch terminal(b,c) to rectify to fourfold voltage.
Accordingly, 110 V power supply is rectified to fourfold 620 V DC voltage and then output from a terminal(X) when an internal capacitor(not shown) in the fourfold-voltage rectifier circuit(1) is fully charged with fourfold DC voltage rectified from said AC input voltage. Said fourfold DC voltage is then applied to an anode terminal(Ad) while a terminal(Y) of the fourfold-voltage rectifier circuit(1) outputs 310 V DC voltage, equal to a half of the fourfold voltage output, which will be applied to a resistor(R1) of a relay driving circuit(2). The resistor(R1) is selected to make a zener diode(ZD1) become conductive when the terminal(Y) of a common fourfold-rectifier circuit(1) outputs 310 V (i.e., after passing through the resistor(R1), 286 V is applied to the ZD1 to make it conductive when the breakdown voltage of the ZD1 is 24 V).
Therefore, the first relay(RY1) is actuated since it experiences a difference of voltage, which is different from the 110 V AC input, between contact(U) and contact(P) on that power supply(AC) is applied. As the relay(RY1) operates to turn on a relay switch thereof, power supply (AC) is applied to a gate of triac (TC1) through a resistor(R5) for trigger voltage so tnat the arxidc(TC1) becomes conductive.
110 V AC applied on the anode of triac(TC1) subsequently flows to a cathode and is then applied on the coil of the second relay(RY2). The second relay(RY2) is operated to connect a relay switch terminal(b) and a terminal(c), and to connect a terminal(e) and terminal(f) respectively, so that an output of the trigger coil(LT) is connected to a terminal(Tr) of the strobe discharge tube(ST1,ST2). The first relay(RY1) can not operate since the zener diode(ZD1) of the relay driving circuit(2) turns off when the voltage offered from the terminal(X,Y) of the well-known fourfold-voltage rectifier circuit(1) is lower than the predetermined voltage because of insufficient charge of the internal capacitor. Accordingly, the triac(TC1) also turns off and results in stoppage of the second relay(RY2), so that the relay switch terminal(a) and the terminal(b), and the terminal(d) and the terminal(e) are respectively connected. Furthermore, the output of the trigger coil(LT) is not connected to the discharge tube(ST1,ST2) while an alarm(AM) makes a sound or illuminates to indicate an insufficient charge in accordance with the formation of a ground path of the power supply applied to the alarm through the capacitor(C4). On the contrary, once the shutter is pressed down to turn on a shutter switch(SW2) of a camera, high voltage offered from the terminal(S) of the high voltage generating circuit (5) for producing typical trigger voltage, is applied to the trigger coil(LT) through the shutter switch(SW2) when the fourfold-voltage rectifier circuit(1) is fully charged and then outputs normal DC(i.e., the terminal(e)and the terminal(f) of the second relay(RY2), and the terminal(b) and the terminal(f) are respectively connected). Trigger voltage generated from the trigger coil(LT) is applied on the trigger terminal(Tr) of the strobe discharge tube(ST1,ST2) through the relay switch terminal(e.f) of the second relay(RY2) while the cathode terminal(Cd) of the strobe discharge tube(ST1,ST2) is provided with a ground point through the relay switch terminals(b,C), so that the strobe discharge tube discharges to radiate the light having suitable luminous intensity to take a photo.
In the case of 220 V power supply input, a 220 V relay(RY3) of the 110/220 V automatic switching circuit(3) is operated to turn on the relay switch. As the triac(TC2) becomes conductive depending on the current that flows to the gate of the triac by the power supply(AC) through the resistor(R4), the fourth relay(RY4) starts to operate. Consequently, as the relay switch terminal(a) and the terminal(b), and the terminal(d) and the terminal(e) are respectively connected, the 220 V power supply(AC) is applied to the primary end terminal of transformer(T1) through the terminals(d,e), so that voltage on the secondary of transformer(T1) is similar to the above case that the power supply is 110 V. Furthermore, in the well-known fourfold-voltage rectifier circuit(1), since the relay switch terminals(a,b) are connected, the double-voltage rectifier circuit(11) and the other double-voltage rectifier circuit(12) are spaced apart from each other. The 220 V power supply applied to the terminals(A,B) is rectified to double voltage through only one double-voltage rectifier circuit(11) and then 620 V output is offered to the terminal(X). Accordingly, it is operated in similar with the case of 110 V power supply because the voltage offered from the respective terminals(X,Y) are 620 V DC and 310 V DC respectively.
The capacitor(C2) arranged in the input of the power supply(AC) prevents spark that can be produced by on/off operation of power switch(SW1).
The optical sensor(4) aims to increase luminous intensity by radiation of the discharge tubes(ST1,ST2) when the another strobe discharge tube, separated from the present invention, is emitted, in other word, the photo-transistor(PT) is turn on by light radiated from the strobe discharge tube, and high voltage offered from the terminal of the high voltage generating circuit(S) is then reduced through a resistor(Rx) having several mega-.omega. when another strobe discharge tube starts to discharge by turning on the switch.
Thereafter, the reduced voltage is applied to the gate of the triac(TC3) through the switch(SW3), a collector of the photo-transistor, and an emitter(wherein, a high resistor is used as the resistor(Rx) to protect the photo-transistor(PT)). In accordance with this, the triac(TC3) becomes conductive and then high voltage generated from the terminal(S) of a well-known high voltage generating circuit(5) is applied to the trigger coil(LT) through the triac(TC3) so that the applied trigger voltage make the strobe discharge tubes(ST1,ST2) discharge in the same manner with the shutter switch(SW2) pressed down. Since this instantaneous operation is activated by light, as soon as another strobe discharge tube starts to discharge, the luminous intensity of light is increased as much as the amount of the additional discharge.
It is necessary to separate the strobe discharge tube(ST1,ST2) from the connector. It is achieved by turning off the switch(SW1) at first, and then stopping the second relay(RY2) from emitting the spark when the discharge tubes(ST1,ST2) become connected or disconnected.
In addition, when the strobe discharge tubes (ST1,ST2) are not radiated in practice through they should be activated by photoflash of another separated strobe discharge tube in outside, i.e., when the strobe discharge tubes(ST1,ST2) are not discharged in sequence, the alarm(AM) does not operate to make a sound and/or light since the contacts of the second relay(RY2) are maintained in the state of (b,c) and (e,f). Consequently, user may know whether the strobes are operated in sequence or not, so that it is possible to re-take a photo when it fails to photograph an object.
The conventional strobe dimmer using a constant-voltage may not ensure good photographing since the color temperature is too high or too low according to the voltage, i.e., when the conventional strobe is adapted to a main light and/or an auxiliary light, the color temperature of the strobe is changed in accordance with the voltage. Wherein, the color temperature is set on the basis of the sun of which the color temperature is 5500.degree. K. This means that fire of 5500.degree. K radiates the same color as the sun. Accordingly, as most film manufacturers make film to present the best color under daylight, 5500.degree. K color temperature is the most preferable to take a photo.
A tungsten lamp can be used as a main light or an auxiliary light according to voltage, i.e., in the case of high voltage, the lamp becomes more bright(colored blue) and is therefore suitable for the main light. while in the case of low voltage, the lamp becomes relatively dark(colored red) so as to be suitable for the auxiliary light. However, an object presents contrasts of light and shade according to the brightness of the lamp, so that it is not preferable to take a good photo, because of dark part colored red.
For example, when two 600 W/s strobe discharge tubes are respectively used as a main light and an auxiliary light for portrait, the main light is set in 600 W/s and the auxiliary light in 200 W/s. The main light is 5800.degree. K and the auxiliary light is 5400.degree. K, while pure white light is 5500.degree. K, so that a part toward the main light is tinted with blue and the other part toward the auxiliary light is tinted with red. This results from the relative high color temperature of the main light so to radiate blue light and the relatively low color temperature of the auxiliary light so as to radiate red light. Consequently, the portrait presents blue color in one check and simultaneously red color in the other check so that it is hard to control the color balance during developing.
If the red color toward the main light is corrected, the other part toward the auxiliary light is tinted with red still more, and the reverse case has a similar drawback, so that it should be developed in in-between tone.
Thereafter, in the conventional lights using simple constant voltage unit, color temperature becomes too high or too low depending on voltage. A right strobe, a left strobe and another strobe(main light, auxiliary light, front light, top light, and spot light, etc.) have different color temperatures respectively so this not ensure good photographing.
Although it is preferable for a general commercial photo to use 5500.degree. K color temperature, 5000.degree. K.about.5300.degree. K color temperature is preferable for a mild image of portrait. A gold coated strobe, which is emitting red color, has been used for a preferable portrait to eliminate blue color radiated from a xenon lamp up to the present. It is necessary to execute a complicated operation to adjust a color temperature by control of the luminous intensity.
Alternatively, since the color temperature is increased or decreased depending on the apparatus that is used for indirect lighting, it is hard to obtain the desired color temperature for photography when a reflector or a light filtering soft-box is used to avoid direct lighting of the strobe. Hence, It is necessary to use a filter determined by MIRED(Micro Reciprocal Degree) calculation measuring the different color temperature of the strobe.
Furthermore, in order to photograph a dark part and a bright part of an object with the same the color temperature, it is necessary to illuminate the dark part from far away, which is quite complicated.